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Common causes of electrical interference:
• Voltage surge, voltage drops, voltage spikes, line faults (damaged cable, bad connections).
• Close proximity to electronic equipment, and/or to power source.
• Noisy motors, relay ‘chatter’.
• Poor dead-band control in process controller providing the signal to the DPS
Suggested remedies:
• Shielding the control cables from the power cables as close proximity of power and control cables is a known cause of signal issues.
• Add a voltage stabilizer/ power conditioner
• As with most things, the higher the quality the process control equipment, the better
Signalling devices and/ or controller issues cause problems for the DPS as the DPS receives the signal sent by the controller. If the device
isn’t correctly configured it can emit rapidly fluctuating signals which causes the controller to constantly adjust its output. The effect of
this can be reduced by adjusting the controller’s dead-band (sensitivity) and other settings.
To identify where the cause of the problem lies:
• Check the output from the physical device (temperature sensor, pressure sensor, any type of transducer).
• Then check the output from the control panel
• Then check the signal at the actuator’s Din plug
0-10V Control Signals:
0-10VDC Control signals are susceptible to issues caused by;
• Cabling issues – voltage drop (cable size, length of run, power supply)
• Electrical interference from motors, relays etc
• 0V (zero volts) is normally the closed position but could be loss of signal (which is why some prefer 2-10V to differentiate between the
two), making diagnosis tricky as it could be a controller fault and it is not sending a signal, or it’s OK and sending a correct 0V.
• Also, check that the 0V is not linked to the power side of the electrical system, it needs an independent supply.
• For unstable signals, a 2200µF capacitor between the +ve and –ve of the 0-10V may help.
Visual checks:
• Often it is not easy to see a fluctuating signal by the naked eye, and the change in control signal can be small – sufficient to cause the
motor to constantly change direction but insufficient to physically move the gears. It is more likely that the fluctuations can only be seen
by checking the signal with a loop calibrator or similar.
